It is well acknowledged that the biocompatibility requirements of successful blood contacting devices exceed those expected of those interfacing with most biological tissues because of the more complex interaction of blood components with these devices. Among the most important types of blood contacting devices, which are noted for their critical functional requirements are synthetic vascular grafts, endovascular stent grafts, and endovascular stents.
Synthetic vascular grafts made primarily of expanded polytetraethylene (E-PTFE) and woven or knitted polyethylene terephthalate (PET) are most commonly used. Synthetic vascular grafts implanted as large vessel replacements have achieved a reasonable degree of success. However, medium- and small-diameter prostheses (less than 6 mm in diameter) loss of patency within several months after implantation is more acute. Graft failure due to thrombosis or intimal hyperplasia with thrombosis is primarily responsible for failure within 30 days after implantation. Intimal hyperplasia formation is the reason for failure within 6 months after surgery. Shortly after implantation, a layer of fibrin and fibrous tissue covers the intimal and outer surface of the prosthesis, respectively. The fibrin is then replaced by a layer of fibroblasts referred to as neointima. In the latter stages, neointimal hyperplasia formation takes place and ultimately results in the occlusion of the vessel in small-diameter grafts. Events leading to occlusion have been related to less than optimal chemical and/or mechanical biocompatibility of the graft-surface and discontinuity of the mechanical properties across the anastomotic site, due to differences in mechanical compliance between the natural vessel and synthetic graft. Accordingly, most of the prior art on synthetic vascular grafts dealt with improving the graft compliance and/or modifying its luminal surface to intervene with events leading to occlusion. However, most, if not all, efforts have been associated with limited success in the small-and medium-diameter grafts. Other unsolved problems of synthetic vascular grafts which require serious attention to optimize their performance include: (1) bleeding at suture needle holes; (2) blood leakage through the graft walls; and (3) infection due to contamination during surgery. These unsolved problems and consistent needs for improving the biocompatibility at the blood-graft interface justified the exploration of the novel sealants and coatings for synthetic grafts subject of this invention. In effect, certain aspects of the present invention deal with similar complications encountered in endovascular stent grafts. Equally important is the fact that most of the events leading to graft occlusion contribute to the failure of endovascular stents placed in the blood vessel to prevent restenosis following angioplasty. A key factor leading to the functional failure of endovascular stents is manifested in post-operative restenosis due, in part, to smooth muscle cell proliferation across the stent. And certain components of the present invention deal with novel corrective measures to stent functional failure and restenosis. Accordingly, the present invention deals with sealants and coatings for synthetic vascular grafts, and endovascular stent grafts that (1) improve the mechanical and barrier properties of vascular grafts; (2) minimize or eliminate events leading to functional failure of endovascular stent grafts and different types of conduit stabilizing stents; (3) are designed to release necessary bioactive agents which prolong the functional performance of the specific device; and/or (4) provide a timely release of antimicrobial agents to prevent and/or treat infection.